GABA neurons in the ventral tegmental area regulate non-rapid eye movement sleep in mice

Abstract The daily sleep/wakefulness cycle is regulated by coordinated interactions between sleep- and wakefulness-regulating neural circuitry. However, the detailed neural circuitry mediating sleep is far from understood. Here, we found that glutamic acid decarboxylase 67 (Gad67)-positive GABAergic neurons in the ventral tegmental area (VTA Gad67+ ) are a key regulator of non-rapid eye movement (NREM) sleep in mice. VTA Gad67+ neurons project to multiple brain areas implicated in sleep/wakefulness regulation such as the lateral hypothalamus (LH) and dorsal raphe nucleus. Chemogenetic activation of VTA Gad67+ neurons promoted NREM sleep with higher delta power whereas optogenetic inhibition of these neurons induced prompt arousal from NREM sleep under highly somnolescent conditions, but not during REM sleep. In vivo fiber photometry recordings revealed that VTA Gad67+ neurons showed the highest population activity in NREM sleep and the lowest activity in REM sleep. Acute brain slice electrophysiology combined with optogenetics revealed that VTA Gad67+ neurons directly innervate and inhibit wake-promoting orexin/hypocretin neurons in the LH by releasing GABA. Taken together, we reveal that VTA Gad67+ neurons play a crucial role in the regulation of NREM sleep.